I made another stab at getting 18.04 working and was successfully only with the minimal Desktop. The server consistently gave dependency errors when using the AMD approved
amdgpu-pro-19.10-785425-ubuntu-18.04.tar
on
ubuntu-18.04.2-desktop-amd64.iso
using rufus to create a USB3 flash install

Tried twice to do full install with 3rd party driver. Both attempts failed and install package made a report to developers.

I then did a minimal desktop but still with 3rd party drivers. This worked but...
"apt-get update" hung at "gdm3" but ctrl-c allowed the update to continue.
I then did the same update again (after a reboot) but this time it got past "gdm3" whatever that is.
I am guessing that something was out of order in the update and whatever was missing got put in
and that is why the gdm3 completed the second time.
I then did
apt-get install build-essential dpkg
as I read somewhere that both were needed.
I then put in openssh and tftpd for remote access
I untarred amdgpu-pro-19.10-785425-ubuntu-18.04.tar
and the install script worked perfectly unlike when I tried the minimal server.
boinc installed just fine but I need to put in a delay as boinc does not see the
five gpus on initial boot.
Somewhere in the above, I had to put in a "sudo dpkg --configure -a"
but I was asked to do that which was nice. I think it was after the ctrl-c